SDL_AudioPostmixCallback(3type)

💖 SDL_AudioPostmixCallback 💖

okay bestie, gather round, because this one is a datatype from the SDL3 DATATYPES era and it is genuinely so fun. it's a callback — the little function that SDL calls for you when the audio is almost out the door.

---

✨ NAME ✨

SDL_AudioPostmixCallback — the callback that fires when data is about to be fed to an audio device. like, the very last stop before your speakers get it. 🎧

---

🌸 SYNOPSIS 🌸

#include <SDL3/SDL_audio.h>

typedef void (SDLCALL *SDL_AudioPostmixCallback)(void *userdata, const SDL_AudioSpec *spec, float *buffer, int buflen);

---

🦋 DESCRIPTION 🦋

so why do you even want this? because it hands you the final mix. the whole thing, all mixed down, right before playback. that's the dream if you're building a visualizer (bars go brrr 📊) or you wanna slap one last effect on the audio before it hits the device. iconic behavior honestly.

⚠️ but listen — this callback must run as quickly as possible. do not block for any significant amount of time, because while you're sitting there thinking about it, you're delaying the submission of data to the audio device, and that causes audio playback problems. we do not want the crunchy sound. 😭

another thing: the postmix callback must be able to handle any audio data format specified in spec. and yeah, that format can literally change between callbacks if the audio device changed. no cap. but here's the good news — this only covers frequency and channel count. the data is always provided here in SDL_AUDIO_F32 format. so at least that part's consistent. periodt. 💅

and the slay detail: this callback runs _after_ logical device gain and audiostream gain have already been applied. which means — and this is the fun part — you can make the output data louder at this point than the gain settings would suggest. main character energy fr fr. 🔥

---

🎀 FUNCTION PARAMETERS 🎀

• userdata — a pointer that the app hands over through SDL_SetAudioPostmixCallback, for its own personal use. it's yours, do what you want with it. 🫶
• spec — the current format of audio that is about to be submitted to the audio device. the vibe check of the moment. ✨
• buffer — the buffer of audio samples about to be submitted. the callback can inspect it and/or modify it. peek at it, remix it, go off. 🎛️
• buflen — the size of buffer, in bytes. 📏

---

🧚 THREAD SAFETY 🧚

heads up: this will run from a background thread owned by SDL. so the application is responsible for locking any resources the callback touches that need to be protected. don't be out here touching shared stuff unprotected, bestie, that's how you get race conditions and a bad time. 💀

---

⭐ AVAILABILITY ⭐

this datatype is available since SDL 3.2.0. baby of the family but already thriving. 🌱

---

🌈 SEE ALSO 🌈

• SDL_SetAudioPostmixCallback(3) — the function that sets this whole thing up. the other half of the duo. 👑

---

and that's the tea, bestie 💜 go make something that sounds good and looks even better. this page came to you from Simple Directmedia Layer, version SDL 3.4.18, filed under SDL_AudioPostmixCallback(3type). mwah. 💅🎀🦋